This invention relates to improved systems and methods for transferring fluids from marine transportation vessels to end users. More specifically, the improvement relates to offshore structures including a single point mooring, regasification facilities, and means for unloading liquefied gases from marine transportation vessels into the regasification facilities. Advantageously, at an offshore structure or tower of this invention, liquefied gas is efficiently regasified for pipeline transport to end users while mooring forces on the marine transportation vessel are minimized.
Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
Marine transportation vessels are frequently used for transporting fluids such as liquefied natural gas (xe2x80x9cLNGxe2x80x9d), i.e., natural gas that has been liquefied at substantially atmospheric pressure and a temperature of about xe2x88x92162xc2x0 C. (xe2x88x92260xc2x0 F.). U.S. Pat. No. 6,085,528 (the xe2x80x9cPLNG Patentxe2x80x9d), having corresponding International Publication Number WO 98/59085 and entitled xe2x80x9cSystem for Processing, Storing, and Transporting Liquefied Natural Gasxe2x80x9d, and U.S. Pat. No. 6,460,721 (the xe2x80x9cComposite Container Patentxe2x80x9d), having corresponding International Publication Number WO 00/57102 and entitled xe2x80x9cImproved Systems and Methods for Producing and Storing Pressurized Liquefied Natural Gasxe2x80x9d, both describe containers and transportation vessels for storage and marine transportation of pressurized liquefied natural gas (PLNG) at a pressure in the broad range of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature in the broad range of about xe2x88x92123xc2x0 C. (xe2x88x92190xc2x0 F.) to about xe2x88x9262xc2x0 C. (xe2x88x9280xc2x0 F.). The PLNG Patent and the Composite Container Patent are hereby incorporated herein by reference.
Offloading of PLNG from a marine transportation vessel at import terminals would likely be accomplished with natural gas. It is expected that loading and unloading of PLNG using such a process would be relatively slow and would require that the marine transportation vessel be berthed at the terminal for a period of days, depending on the PLNG cargo capacity of the marine transportation vessel.
Since PLNG is an emerging technology, commercial import terminals for PLNG are not available. However, in most cases where there is a need for single point mooring of ships with process facilities nearby, as is the case with PLNG, the facilities have been installed on a separate platform or on a floating hull to which the ship is then moored in tandem. These are the usual solutions because they are often in deepwater where a tall tower with a large horizontal mooring load would combine to produce a very high overturning moment and require a very costly structure. However, import terminals are not always in deep water. In shallow water, a different scenario arises. The offshore mooring structure, such as a single point mooring tower, is often close enough to shore whereby a subsea pipeline connected to an onshore process facility is typically a good economic means for processing fluids unloaded from a ship. However some fluids do not lend themselves to subsea pipeline transport. This is particularly the case with very cold or cryogenic fluids, for which subsea pipeline designs are still being developed, and will themselves be quite costly.
Some designs have been proposed to solve the aforementioned deepwater and shallow water problems by installing regasification process facilities on each of a set of specially built ships (e.g., U.S. Pat. No. 6,089,022, entitled xe2x80x9cRegasification of Liquefied Natural Gas (LNG) Aboard A Transport Vesselxe2x80x9d). This design could allow delivery of gas from the transportation vessel to a subsea pipeline for long distance transmission, but a set of regasification facilities is required on each transportation vessel or ship. Regasification facilities onboard each ship would require ship modifications and add to the cost of both facilities and ships. Additionally, high pressure subsea hoses that can be easily connected/disconnected from standard tankers have not yet been devised. Therefore, a tanker with onboard regasification facilities cannot discharge directly to a subsea line through hoses or even a floating buoy system. An offshore structure is still required. Some shipping companies have proposed discharge of gas through submerged turrets connected into the bottom of the ship""s hull (avoiding the need for an offshore structure); but turret arrangements require expensive modifications to the ship""s hull. It is desirable to have a system for cost effective delivery of a liquefied gas, such as pressurized liquefied natural gas, from a transport vessel to a subsea pipeline in gaseous form.
Therefore, an object of this invention is to provide cost effective offshore facilities for offloading liquefied gases into pressurized gas transmission lines. Other objects of this invention will be made apparent by the following description of the invention.
Consistent with the above-stated objects of the present invention, an offshore facility is provided that comprises one or more decks upon which are located: (a) regasification facilities; (b) single point mooring means for mooring a ship that is carrying a liquefied gas; (c) means for offloading said liquefied gas into said regasification facilities; and (d) means for transferring gas from said regasification facilities to a gas transport pipeline.